1. Technical Field
Embodiments of the present invention generally relate to a roller including a cylindrical body and a press-fit member fitted in at least one of openings at both ends of the cylindrical body, and a developing roller including the cylindrical body and the press-fit member; and further relate to a developing device, a process cartridge, and an image forming apparatus including the developing roller.
2. Description of the Background Art
Conventionally, image forming apparatuses, such as copiers, facsimile machines, printers, and multifunction machines (so-called multifunction peripherals or MFPs) having at least two of coping, printing, facsimile transmission, plotting, and scanning capabilities, employ a roller including a cylindrical body and a member (i.e., a press-fit member) fitted in at least one of openings of the cylindrical member by press-fit. Such rollers typically rotate upon application of driving force to the press-fit member, and rotational deviation or runout may arise in rotation of the roller if the center of rotation of the press-fit member is deviated from the axis of the cylindrical body.
For example, such rollers are used as developing rollers in image forming apparatuses. If runout in rotation of the developing roller is significant, density unevenness arises in image development, and density of images formed on sheets of recording media becomes uneven. Accordingly, it is preferred to precisely align the position of the center of rotation of the press-fit member with the axis of the cylindrical body to reduce the runout in rotation. Additionally, a relatively large amount of torque is loaded to the connection between the cylindrical body and the press-fit member at the start of rotation, and it is desirable that such rollers have a high degree of durability against the torque load.
There are various rollers having a cylindrical body and a press-fit member. For example, in JP-H06-324609-A, a groove parallel to the axis is provided in an inner face of the cylindrical body, and a projection to fit in the groove is formed on an outer circumferential face of the press-fit member. Additionally, in JP-H07-020674-A, a female screw is provided to the inner face of the cylindrical body, and a male screw to engage the female screw is provided to the outer circumferential face of the press-fit member. Yet additionally, in JP-H09-086712-A, a projection parallel to the axis is provided to the inner face of the cylindrical body to fit in a groove in the outer circumferential face of the press-fit member, and connection therebetween is enhanced using glue.